A solid oxide fuel cell (hereinafter sometimes referred to as SOFC) system usually includes a reformer for reforming a hydrocarbon-based fuel, such as kerosene and city gas, to generate a hydrogen-containing gas (reformed gas), and an SOFC for electrochemically reacting the reformed gas and air for electric power generation.
The SOFC is usually operated at a high temperature of 550 to 1000° C.
Various reactions, such as steam reforming (SR), partial oxidation reforming (PDX), and autothermal reforming (ATR), are used for reforming, and heating to a temperature at which catalytic activity is exhibited is necessary for using a reforming catalyst.
Steam reforming is a very largely endothermic reaction. Also, the reaction temperature of the steam reforming is 550 to 750° C., which is relatively high, and the steam reforming requires a high temperature heat source. Therefore, an internal reforming SOFC is known in which a reformer (internal reformer) is installed near an SOFC, and the reformer is heated mainly using radiant heat from the SOFC as a heat source (Patent Document 1).
Also, proposals on the load following operation of a fuel cell system are made in Patent Documents 2 and 3.    Patent Document 1: JP2004-319420A    Patent Document 2: JP2001-185196A    Patent Document 3: JP2006-32262A